The Forge of God is Greg Bear's best novel and one of the best, if not the best, alien invasion novels written since H.G. Wells got the ball rolling with The War of the Worlds. Long but not overlong, the story is told with a grim and powerful sense of inevitability that gives its climax a tremendous jolt of authenticity and emotional force. And despite the fact you pretty much know how the book is going to end by the time you're halfway through, it still has the power to bring readers to tears. The novel is also a fine melding of hard SF and character driven, "triumph of the human spirit" drama, related without any Hollywoodish sentimentalism or treacly preachifying. Christ, how did Greg Bear pull this off anyway!?
The plot kicks off with the discovery of various geological anomalies — like mountains that weren't there just a little while ago — peppered around the Earth in remote locations like the Australian outback and Death Valley. It is gradually discovered that these strange oddities are in fact artificial creations planted here by extraterrestrials; the Death Valley location even coughs up a real ET, who gives the bewildered Americans (and soon the world) the frightening story that the Earth is under siege by an unknown alien force that literally eats worlds from the core out, like worms in an apple. Worse, it seems that there is no defense — zip, zilch, nada — against this destruction. The Earth itself is faced with an extinction event about which it can do nothing.
The news stuns the world; the fact that the devoutly religious President of the U.S. comes out publically and and tells everyone we're all fucked does nothing for humanity's morale, to say the least. But then an unpredicted player enters the fray; another alien race, which has been scouring space seeking out the planet-eaters, arrives in the solar system. Earth has an ally, and though they say they can do nothing to stop the imminent destruction of the planet, they set about rounding up thousands of human candidates (as well as records of Earth's history, literature, etc.) for rescue in "arks."
Throughout The Forge of God, Greg Bear makes remarkable storytelling decisions that keep his tale from sloshing through the quagmire of formula predictability. Most interesting is his depiction of humanity's reaction to news of its upcoming extinction; whereas the clichéd approach would lead towards riots, chaos, and destruction, Bear very convincingly portrays us exhibiting everything from plain old denial to overwrought religious revivalism that actually embraces the upcoming apocalypse as the will of God. "Life goes on," sadly intones one character. Faced with the inevitable, most of Bear's people fall back upon introspection, a final devotion to family, friends, loved ones, those crucial memories that define our lives. And all of this is thankfully depicted without mawkishness of any kind. Of course, there are many who try to fight for the Earth; plans are made secretly to nuke the Death Valley invader. And while all this is going on, a select group of people, conscripted telepathically by our mysterious saviors, are moving resolutely to get the arks ready before the Earth's final hours draw nigh.
It is particularly interesting that Bear chose not to identify firmly either the Earth's destroyers or its rescuers. Such a choice might annoy hard-SF purists who insist upon solid explanations for absolutely everything; yet as it stands, the mystery surrounding both good and evil aliens puts the reader squarely on the same playing field as the novel's characters — helpless, frightened, always tense.
But what is most powerful here is quite simply Bear's prose. Very few hard-SF epics can match the stunning power of this novel's last fifty pages. Even the most jaded readers should allow themselves to feel the awe of what's being presented here. If you can't do it, you might as well give up reading as a hobby altogether. You just don't get it.
In this humble reviewer's estimation, this is the novel that brought Greg Bear into the same league as the Masters: Asimov, Clarke, Heinlein, Herbert, Niven, Sturgeon. Followed Anvil of Stars.